Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see
Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Information About BGP 4 Soft Configuration

BGP Session Reset

Whenever the routing policy changes due to a configuration change, BGP peering sessions must be reset by using the
clearipbgp command. Cisco software supports the following three mechanisms to reset BGP peering sessions:

Hard reset—A hard reset tears down the specified peering sessions including the TCP connection and deletes routes coming from the specified peer.

Soft reset—A soft reset uses stored prefix information to reconfigure and activate BGP routing tables without tearing down existing peering sessions. Soft reconfiguration uses stored update information, at the cost of additional memory for storing the updates, to allow you to apply new BGP policy without disrupting the network. Soft reconfiguration can be configured for inbound or outbound sessions.

Dynamic inbound soft reset—The route refresh capability, as defined in RFC 2918, allows the local device to reset inbound routing tables dynamically by exchanging route refresh requests to supporting peers. The route refresh capability does not store update information locally for nondisruptive policy changes. It instead relies on dynamic exchange with supporting peers. Route refresh must first be advertised through BGP capability negotiation between peers. All BGP devices must support the route refresh capability. To determine if a BGP device supports this capability, use the
showipbgpneighbors command. The following message is displayed in the output when the device supports the route refresh capability:

Received route refresh capability from peer.

The
bgpsoft-reconfig-backup command was introduced to configure BGP to perform inbound soft reconfiguration for peers that do not support the route refresh capability. The configuration of this command allows you to configure BGP to store updates (soft reconfiguration) only as necessary. Peers that support the route refresh capability are unaffected by the configuration of this command.

Perform this task to configure inbound soft reconfiguration using the
bgpsoft-reconfig-backup command for BGP peers that do not support the route refresh capability. BGP peers that support the route refresh capability are unaffected by the configuration of this command. Note that the memory requirements for storing the inbound update information can become quite large.

9. Repeat Steps 6 through 8 for every peer that is to be configured with inbound soft reconfiguration.

10.exit

11.route-mapmap-name [permit |deny] [sequence-number]

12.setlocal-preferencenumber-value

13.end

14.showipbgpneighbors [neighbor-address]

15.showipbgp [network] [network-mask]

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

routerbgpautonomous-system-number

Example:

Device(config)# router bgp 45000

Enters router configuration mode for the specified routing process.

Step 4

bgplog-neighbor-changes

Example:

Device(config-router)# bgp log-neighbor-changes

Enables logging of BGP neighbor resets.

Step 5

bgpsoft-reconfig-backup

Example:

Device(config-router)# bgp soft-reconfig-backup

Configures a BGP speaker to perform inbound soft reconfiguration for peers that do not support the route refresh capability.

This command is used to configure BGP to perform inbound soft reconfiguration for peers that do not support the route refresh capability. The configuration of this command allows you to configure BGP to store updates (soft reconfiguration) only as necessary. Peers that support the route refresh capability are unaffected by the configuration of this command.

All the updates received from this neighbor will be stored unmodified, regardless of the inbound policy. When inbound soft reconfiguration is done later, the stored information will be used to generate a new set of inbound updates.

Step 8

neighbor {ip-address |
peer-group-name}
route-mapmap-name {in |
out}

Example:

Device(config-router)# neighbor 192.168.1.2 route-map LOCAL in

Applies a route map to incoming or outgoing routes.

In this example, the route map named LOCAL will be applied to incoming routes.

Step 9

Repeat Steps 6 through 8 for every peer that is to be configured with inbound soft reconfiguration.

—

Step 10

exit

Example:

Device(config-router)# exit

Exits router configuration mode and enters global configuration mode.

Step 11

route-mapmap-name [permit |deny] [sequence-number]

Example:

Device(config)# route-map LOCAL permit 10

Configures a route map and enters route-map configuration mode.

In this example, a route map named LOCAL is created.

Step 12

setlocal-preferencenumber-value

Example:

Device(config-route-map)# set local-preference 200

Specifies a preference value for the autonomous system path.

In this example, the local preference value is set to 200.

Step 13

end

Example:

Device(config-route-map)# end

Exits route-map configuration mode and enters privileged EXEC mode.

Step 14

showipbgpneighbors [neighbor-address]

Example:

Device# show ip bgp neighbors 192.168.1.2

(Optional) Displays information about the TCP and BGP connections to neighbors.

Note

Only the syntax applicable to this task is used in this example. For more details, see the
Cisco IOS IP Routing: BGP Command Reference.

Step 15

showipbgp [network] [network-mask]

Example:

Device# show ip bgp

(Optional) Displays the entries in the BGP routing table.

Note

Only the syntax applicable to this task is used in this example. For more details, see the
Cisco IOS IP Routing: BGP Command Reference.

Examples

The following partial output from the
showipbgpneighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.2.1. This peer supports route refresh.

The following partial output from the
showipbgpneighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.3.2. This peer does not support route refresh so the soft-reconfig inbound paths for BGP peer 192.168.3.2 will be stored because there is no other way to update any inbound policy updates.

The following sample output from the
showipbgp command shows the entry for the network 172.17.1.0. Both BGP peers are advertising 172.17.1.0/24, but only the received-only path is stored for 192.168.3.2.

Examples: BGP Soft Reset

The following examples show two ways to reset the connection for BGP peer 192.168.1.1.

Example: Dynamic Inbound Soft Reset

The following example shows the command used to initiate a dynamic soft reconfiguration in the BGP peer 192.168.1.1. This command requires that the peer support the route refresh capability.

clear ip bgp 192.168.1.1 soft in

Example: Inbound Soft Reset Using Stored Information

The following example shows how to enable inbound soft reconfiguration for the neighbor 192.168.1.1. All the updates received from this neighbor will be stored unmodified, regardless of the inbound policy. When inbound soft reconfiguration is performed later, the stored information will be used to generate a new set of inbound updates.

Additional References

Related Documents

Standards and RFCs

Standard/RFC

Title

RFC 2918

Route Refresh Capability for BGP-4

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

Feature Information for BGP 4
Soft Configuration

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Table 1 Feature Information for BGP 4
Soft Configuration

Feature Name

Releases

Feature
Information

BGP 4 Soft
Configuration

BGP 4 Soft
Configuration allows BGP4 policies to be configured and activated without
clearing the BGP session, hence without invalidating the forwarding cache.